Demonstration of three-photon entanglement on a photonic chip

Photonic quantum computers are computing tools that utilize quantum physics and use light particles (i.e. photons) as information processing units. These computers may eventually surpass traditional quantum computers in speed and transmit information over greater distances.

Despite their promise, photonic quantum computers have yet to achieve expected results, in part because of the inherently weak interactions between individual photons.In a paper published in Physical Review LettersResearchers at the University of Science and Technology of China have demonstrated a large cluster state, three-photon entanglement, that could facilitate quantum computing in photonic systems.

“Photonic quantum computing holds great promise due to its advantages of operating at room temperature and minimal decoherence,” Hui Wang, co-author of the paper, told Phys.org.

“However, the inherent challenge lies in the weak interactions between single photons, hindering the realization of deterministic two-qubit gates necessary for scalability. To address this problem, the past two decades have seen the emergence of fusion and Penetration concept.

Past research has shown that fusion and percolation can be scalable ways to achieve quantum computing in photonic systems without the need for deterministic entanglement gates, such as those required for superconducting qubits and trapped ions. As part of their research, Wang and his colleagues employed a strategy that requires fusing small resource states, such as the 3-GHZ state they demonstrated, into large-scale cluster states suitable for enabling measurement-based quantum computing.

“The penetration theorem shows that if the success probability of a fusion gate exceeds a certain threshold, success can be achieved,” Wang said.

“In this framework, the initial stage involves generating the necessary resource states, the smallest elementary state being the three-photon Greenberger-Horne-Zeilinger (3-GHZ) state. There are two main methods for deterministic 3-GHZ state generation: (i) Utilizing single-photon emitters like quantum dots, while theoretically deterministic, current technologies face efficiency limitations; (ii) generate entangled clusters nearly deterministically in a predictable manner, enabling the generation of entangled clusters without disturbing the target; In case of status, immediate verification is successful.

Of the two methods for generating 3-GHZ states, the near-deterministic generation of entangled clusters in the manner foreshadowed currently appears to be the most promising. Using this approach, the researchers were able to achieve this state from a single photon source in a photonic chip.

Their work is an important milestone on the road to achieving fault-tolerant photonic quantum computing. Specifically, their efforts could accelerate the development of large-scale optical quantum computers that rely on the 3-GHZ state to process quantum information.

“Our experimental setup requires the injection of six single photons into a 10-mode passive interferometer,” Wang explained.

“Our implementation utilizes InAs/GaAs quantum dots as single-photon sources. Remarkably, this is the most advanced single-photon source in any physical system. The programmable interferometer from Quix shows overall efficiency through application-specific For a single transition, the final output state on ports 1-6 appears as the 3-GHZ state predicted by dual-rail encoding, depending on the detection of single photons in both ports and in one of the ports.

The first reports of single photons date back to 1986, while the first entangled photon pair was achieved in 2010. Large cluster states that enable fault-tolerant, measurement-based quantum computing using photonic wafers.

It is worth noting that this paper was published around the same time as two related studies by other teams, respectively published in Physical Review Letters and Nature Photonics, and other impressive results were obtained. Taken together, these advances show that we are one step closer to effectively realizing fault-tolerant photonic quantum computers.

“Demonstration of a fusion gate beyond the penetration threshold using eight single photons is achievable in the foreseeable future,” Wang added.

“Based on the success of the 3-GHZ state proposed in this study, multiple 3-GHZ resource states can be merged to form a wider range of entangled states. In addition, exploration of large-scale entangled state generation on integrated quantum optical platforms is in progress.”

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